UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS. 


COLLEGE  OF  AGRICULTURE. 


AGRICULTURAL  EXPERIMENT  STATION. 


FUMIGATION  DOSAGE. 


By  C.  W.  WOODWORTH. 


The  Fumigator  in  the  Act  of  Charging  a  Generator 
Under  the  Hoop  Tent. 


BULLETIN  No.  152 

(Berkeley,  June,  1903,) 


SACRAMENTO: 
w.  w.  shannon,      :      :      :      :      SUPERINTENDENT  state  printing. 

1903. 


BENJAMIN  IDE  WHEELER,  Ph.D.,  LL.D.,  President  of  the  University. 

EXPERIMENT  STATION  STAFF. 

E.  W.  HILGARD,  Ph.D.,  LL.D.,  Director  and  Chemist. 

E.  J.  WICKSON,  M.A.,  Horticulturist,  and  Superintendent  of  Central  Station  Grounds. 

W.  A.  SETCHELL,  Ph.D.,  Botanist. 

ELWOOD  MEAD,  M.S.,  C.E.,  Irrigation  Engineer. 

R.  H.  LOUGHRIDGE,  Ph.D.,  Agricultural  Geologist  and  Soil  Physicist.    (Soils  and  Alkali.) 

C.  W.  WOODWORTH,  M.S.,  Entomologist. 

M.  E.  JAFFA,  M.S.,  Assistant  Chemist.    (Foods,  Fertilizers.) 

G.  W.  SHAW,  M.A.,  Ph.D..  Assistant  Chemist.     (Soils,  Beet-Sugar.) 

GEORGE  E.  COLBY,  M.S.,  Assistant  Chemist.    (Fruits,  Waters,  Insecticides.) 

RALPH  E.  SMITH,  B.S.,  Plant  Pathologist. 

A.  R.  WARD,  B.S.A.,  D.V.M.,  Veterinarian,  Bacteriologist. 

E.  H.  TWIGHT,  B.Sc,  Diploma  E. A.M.,  Viticulturist. 

E.  W.  MAJOR,  B.Agr.,  Dairy  Husbandry. 

A.  V.  STUBENRAUCH,  M.S.,  Assistant  Horticulturist  and  Superintendent  of  Substations. 

WARREN  T.  CLARKE,  B.S.,  Assistant  Field  Entomologist. 

H.  J.  QUAYLE,  B.S.,  Assistant  Entomologist. 

H.  M.  HALL,  M.S.,  Assistant  Botanist. 

GEORGE  ROBERTS,  M.S.,  Assistant  Chemist  in  Charge  Fertilizer  Control. 

C.  A.  TRIEBEL,  Ph.G.,  Student  Assistant  in  Agricultural  Laboratory. 

C.  A.  COLMORE,  B.S.,  Clerk  to  the  Director. 

EMIL  KELLNER,  Foreman  of  Central  Station  Grounds. 


JOHN  TUOHY,  Patron,  ) 

y  Tulare  Substation,  Tulare. 
JULIUS  FORRER,  Foreman,  ) 

R.  C.  RUST,  Patron,  >  

>•  Foothill  Substation,  Jackson. 
JOHN  H.  BARBER,  Foreman,  ) 

S.  D.  MERK,  Patron,  ) 

„    _    ,  .      ,  >  Coast  Range  Substation,  Paso  Robles. 

J.  H.  OOLEY,  Workman  in  charge,  ) 

-on,  ) 

Y  Southern  California  Substation,   < 
J.  W.  MILLS,  Foreman,      )  {  Ontario. 


S.  N.  ANDROU3,  Patron,  )  (Pomona. 

J.  W.  MILLS,  Foreman,      j 

V.  C.  RICHARDS,  Patron, 

T.  L.  BOHLENDER, 

ROY  JONES,  Patron, 

WM.  SHUTT,  Forema 


Forestry  Station,  Chico 
T.  L.  BOHLENDER,  m  charge   ' 


1 

t   Forestry  Station,  Santa  Monica. 


The  Station  publications  (Reports  and  Bulletins)  will  be  sent  to  any 
citizen  of  the  State  on  application^  so  long  as  available. 


FUMIGATION  DOSAGE. 


Practical  fumigators  in  California  have  been  notoriously  at  variance 
with  each  other  in  their  estimation  of  the  dose  of  cyanide  required  for  a 
tent  of  any  given  size.  They  all  uniformly  claim  that  they  endeavor 
to  place  under  each  tent  all  that  can  be  used  with  safety  to  the  tree. 
Those  using  the  larger  dosage  often  claim  that  the  others  are  not  using 
enough,  and  these,  on  the  other  hand,  usually  maintain  that  under 
their  local  conditions  a  larger  dosage  is  impossible  without  injury.  The 
common  method  employed  by  fumigators  to  verify  the  correctness  of 
their  estimates  is  to  examine  the  orchards  the  day  after  fumigation,  and 
they  are  satisfied  if  here  and  there  slight  traces  of  injury  to  foliage  can 
be  seen. 

It  was  supposed  by  us  that  these  differences  of  practice  among  fumi- 
gators were  really  justified  by  the  facts,  and  the  present  investigation 
was  undertaken  to  determine  and  record  the  best  practice  of  the  various 
regions.  One  would  naturally  expect  that  after  all  these  years  there 
would  have  come  to  be  certain  recognizable  standards  based  upon 
practical  experience. 

For  the  purpose  of  determining  the  actual  practice,  Mr.  J.  S.  Hunter 
was  sent  into  the  field  and  spent  nearly  two  months  visiting  practically 
every  fumigation  outfit  operating  in  the  State,  making  measurements  of 
the  tented  trees  and  recording  the  doses  assigned  to  them.  In  this  way 
we  have  secured  dosage  and  measurements  of  2,314  trees,  representing 
the  judgment  of  thirty  fumigators. 

The  data  thus  obtained  have  failed  to  indicate  that  the  practical 
experience  has  resulted  in  a  satisfactory  solution  of  the  problems  of 
dosage.  We  have  found,  as  will  be  shown  below,  that  the  judgment  of 
all  the  fumigators  is  thoroughly  unreliable.  It  is  doubtless  a  physical 
impossibility  to  guess  with  any  degree  of  accuracy  the  capacity  of  a  tent. 

The  remarkable  thing  is  that  the  results  obtained  in  fumigation  in 
the  killing  of  scale  insects  have  been  uniform  enough  to  be  fairly  satis- 
factory. They  show  that  the  process  of  fumigation  allows  a  very  wide 
margin  between  efficiency  against  the  insect  and  danger  to  the  plant. 
A  reformation  in  the  method  of  estimating  the  dose  could  not  fail  either 
to  greatly  diminish  the  cost  of  the  chemicals  used,  or  to  improve 
markedly  the  certainty  and  uniformity  of  the  results. 


4  UNIVERSITY    OF   CALIFORNIA — EXPERIMENT   STATION. 

THE    METHOD     OF    MEASUREMENT. 

The  method  used  in  making  the  measurements  of  the  tents  in  this 
study  was  quite  simple,  and  consisted  in  the  use  of  a  fishing-rod  and 
wire  line.  A  piece  of  electric  drop-light  insulated  cord  was  used  as  the 
line.  This  consists  of  a  cable  of  many  fine  copper  wires  covered  with 
thread,  which  gives  greater  flexibility  and  is  less  liable  to  kink  than  a 
simple  wire. 

The  line  was  marked  off'  into  one-meter  lengths  by  knots.  The 
metric  system  was  used  because  of  convenience  in  calculation. 

The  rod  employed  was  the  ordinary  jointed  fishing-rod,  which  could 
be  disconnected  for  transportation  and  adjusted  to  different  heights  of 


Fig.  1.    The  method  of  measuring  tents  employed  in  securing  the  data  discussed  in  this  bulletin. 

trees.  The  sections  of  the  rod  were  marked  off  into  centimeters  for  use 
in  connection  with  the  line  in  making  the  measurements. 

The  procedure  in  making  the  measure  of  a  tent  is  as  follows:  Having 
first  attached  the  line  at  about  its  middle  to  the  end  of  the  rod,  one  end 
of  the  former  is  made  fast  to  the  tent.  The  most  convenient  way  to 
accomplish  this  was  found  to  be  by  means  of  a  hook,  like  a  fish-hook 
from  which  the  barb  had  been  removed.  The  most  convenient  place  of 
attachment  was  at  a  point  one  meter  from  the  ground. 

After  attaching  one  end  of  the  line  to  the  tent  the  rest  of  that  half  is 
caused  to  lie  up  to  and  over  the  center  and  top  of  the  tent  by  means  of 
the  rod.  The  one  making  the  measurement  then  walks  around  to 
the  opposite  side  of  the  tent,  rod  in  hand,  holding  the  line  constantly 
in  position  over  the  top.     The  other  end  of  the  line  is  carried  around 


FUMIGATION    DOSAGE.  O 

the  tent  at  the  same  time  and  is  then  drawn  taut,  measuring  the  last 
fraction  of  a  meter  by  means  of  the  graduation  on  the  lower  joint  of  the 
rod.  Adding  now  one  meter,  the  distance  the  first  end  is  from  the 
ground,  we  have  the  measurement  of  the  distance  over  the  top  of  the 
tent  from  the  ground  on  one  side  to  the  ground  on  the  other. 

A  second  measurement  was  then  taken  by  throwing  the  line  off  the 
top  of  the  tent  by  means  of  the  rod  and  holding  it  so  that  as  the  meas- 
urer proceeds  around  the  tent  to  the  point  where  the  line  is  attached,  it 
will  encircle  the  tent  at  a  point  about  one  meter  from  the  ground.  The 
end  of  the  rod  is  again  brought  into  requisition  and  the  last  fraction  of 
meter  read  in  centimeters. 

Both  measurements  are  thus  made  by  one  person  in  a  single  trip 
around  the  tent.  Mr.  Hunter  found  that  he  was  able,  after  a  little 
practice,  to  measure  as  rapidly  as  the  tents  could  be  shifted.  This  we 
believe  is  much  more  rapid  than  is  possible  by  any  other  method  that 
has  ever  been  used  for  this  purpose.  It  may,  however,  be  more  accurate 
than  would  be  needed  in  actual  fumigation  practice,  and  the  method 
suggested  below  is  therefore  more  available.  Some  method  of  measure- 
ment, however,  should  by  all  means  be  adopted. 

CALCULATION    OF   VOLUME. 

The  shapes  of  trees  differ  very  greatly,  and  are,  indeed,  always  more 
or  less  irregular.  The  exact  calculation  of  the  volume  of  a  tent  is  a 
very  difficult  matter  and  is  really  never  attempted.  Two  dimensions 
are  measured  and  the  tent  calculated  as  a  regular  figure.  The  regular 
figure  that  comes  nearest  to  the  shape  of  a  tented  tree  is  that  of  a 
cylinder  surmounted  by  a  hemisphere.  The  mathematical  formulas  for 
the  volume  of  a  tent  of  this  shape  are: 


^(A-0and£(o-^) 


In  the  first  formula,  h  is  the  height  and  r  one  half  the  diameter. 
These  are  the  dimensions  usually  given  by  writers  on  fumigation,  but 
are  not  the  measurements  most  easily  made.  The  writer  suggested,  in 
Bulletin  No.  122  of  this  Station,  the  two  measurements  that  were 
employed  in  getting  the  data  upon  which  this  study  is  based.  These 
measurements  are  indicated  by  c,  circumference,  and  o,  the  distance  over 
the  top  of  the  tent,  in  the  second  formula  above. 

The  actual  capacity  of  tents  of  various  dimensions  was  determined 
by  using  the  diagram,  Fig.  2,  the  curves  giving  the  volume  in  steres — 
that  is,  in  cubic  meters.  A  stere  is  approximately  35^  cubic  feet.  By 
the  use  of  this  diagram  one  may  readily  determine  the  volume  of  a  tent 
if  he  have  the  dimensions  according  to  either  method  of  measuring,  and 
in  either  the  common  or  the  metric  system.     The  two  oblique  lines 


6 


UNIVERSITY    OF   CALIFORNIA EXPERIMENT    STATION. 


represent  the  range  actually  found- in  the  shape  of  the  trees  being  fumi- 
gated.    The  curved  lines  show  the  various  volumes  in  the  cube  of  the 

Distance  over  top  of  Tent 


Fig.  2.    Diagram  for  calculating  volume  of  fumigation  tents. 

unit  of  measurement.     Thus,  a  measurement  made  in  yards  would  give 
the  volume  of  a  tent  in  cubic  yards. 


FUMIGATION    DOSAGE.  7 

The  theoretical  shape  of  tent  for  which  all  these  calculations  are 
made  represents  the  largest  possible  volumes  for  the  given  dimensions. 
Any  variation,  therefore,  due  to  the  irregularity  of  the  tree  decreases 
the  actual  volume  of  the  tent.  This  is  on  the  safe  side,  since  the  all- 
important  thing  in  fumigation  is  to  have  the  dose  strong  enough  to 
insure  the  death  of  the  insects. 


LOCAL   VARIATION. 

The  difference  in  the  practice  of  different  fumigators  is  very  evident 
upon  the  most  cursory  examination  of  the  data  obtained,  but  the  com- 
parison of  the  data  in  a  way  that  will  eliminate  other  causes  of  variation 
than  the  one  under  immediate  consideration  is  far  from  easy.  In  order 
to  ascertain  if  there  is  any  variation  distinctly  associated  with  localities, 
comparisons  were  made  between  the  recorded  dosage  of  the  same  sized 
tents  as  estimated  by  the  various  fumigators.  The  trees  varied  so  in 
height  in  the  different  orchards  that  in  some  cases  most  of  the  treated 
trees  were  below  this  size  and  in  other  cases  above,  indeed  quite  a 
number  had  to  be  left  out  altogether  in  this  comparison.  The  dimension 
chosen  for  the  comparison  of  localities  was  ten  steres,  and  in  the  table 
that  follows  all  measurements  indicating  the  size  between  nine  and 
eleven  steres  are  included: 


Ounces  Used. 


Number 

Locality.  of 

Trees. 

Ventura  County — 

Filmore 12 

Los  Angeles  County- 
Pasadena  _ _.  19 

Sunny  Slope.. _ 1 

Arcadia 9 

Duarte _ 11 

Covina  (1) 2 

Covina(3).._ 11 

Covina(4) ._ 2 

Covina(5) 1 

Glendora _ _ _  3 

Pomona 1 

San  Bernardino  County- 
Ontario  (1) 6 

Ontario  (2) 6 

Ontario  (3) 2 

Ontario  (4) 2 

Orange  County— 

Placentia 6 

Anaheim _. 2 

Santa  Ana 14 

Orange  (1) _ 1 

Orange  (2) 12 

Tustin 2 

San  Diego  County — 

Escondido  .  2 

National  City _. 9 


Range. 


Minimum. 

Maximum. 

DO 

2 

3 

2K 

3^ 

2.9] 

2M 

2K 

2.5 

3K 

5 

3.9 

4K 

5 

4.8 

4 

4 

4.0 

3 

4 

3.5 

4 

4K 

4.3 

2K 

2M 

2.5 

4 

5 

4.7 

3 

3 

3.0  J 

3 

4 

3.51 

3 

4 

3.3  ! 

3 

3 

3.0  ( 

3 

3 

3.0  J 

4 

4K 

4,7  1 

4 

4 

4.0 

3 

6 

4.8 

7K 

7K 

7.5 

3 

6 

4.8 

3 

4 

3.5  J 

1 

1 

1.0  J 

2K 

3y2 

3.0  f 

Average 
Dose. 


2.4 


3.6 


3.2 


4.8 


2.0 


8  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION. 

Riverside  County  is  omitted  from  the  above  table,  since  we  have  no 
estimates  of  dosage  for  trees  as  small  as  those  included  in  the  table. 
The  arrangement  of  the  table  by  counties  is  quite  natural,  as  will  be 
seen  by  the  accompanying  map.     (Fig.  3.) 

The  small  dosage  in  Ventura  and  San  Diego  counties  may  account  in 
part  for  the  disfavor  in  which  the  process  is  held  by  many  orchardists  of 
those  districts.  It  is  at  least  interesting  to  note  that  in  the  counties 
where  the  process  is  least  known  the  dosage  is  the  smallest. 

The  largest  dosage  is  in  the  county  where  the  orchardists  to  the 
largest  extent  manipulate  their  own  tents,  or  rather  have  done  so  in  the 
past.     Most  of  the  work  here  as  elsewhere  is  now  done  by  contract. 

The  greatest  uniformity  is  in  San  Bernardino  County,  where  the 
county  inspection  appears  to  have  borne  fruit  in  a  way  that   should 


SAN 

BERNARDINO 

CO 


MAP 
SHOWING  LOCATION 


.Escondido 


ORCHARD  FUMIGATION  WORK  \       ^Q 

CO 
CALIFORNIA  ^tic^i  city 

Fig.  3. 

gratify  the  orchardists  of  that  county.  As  a  contrast  to  this  stands  Los- 
Angeles  County.  The  parts  of  these  counties  in  which  fumigation  is 
practiced  lie  immediately  adjacent  to  each  other,  and  the  average  dosage 
is  about  the  same.  The  average  is  slightly  higher  than  in  the  former 
county,  but  some  fumigators  run  very  low  and  others  very  high  in  their 
estimates.  Here  the  work  is  often  of  the  most  satisfactory  sort,  and  at 
other  times  but  little  good  seems  to  be  done.  The  measurements  suggest 
a  very  possible  explanation  of  the  irregularity  of  the  results  obtained. 
A  very  exhaustive  study  of  the  killing  dose  of  cyanide  gas  should  be 
provided  for  the  coming  fumigation  season,  and  the  desirability  of  a 
very  close  inspection  of  fumigation  operations  is  also  evident. 

PERSONAL    VARIATION. 

While  fumigators  of  a  locality  may  come  to  have  some  degree  of 
agreement  in  the  average  size  of  the  dose  employed,  each  one  exhibits  a 
great  deal  of  irregularity  in  his  judgment  of  the  size  of  the  trees.  One 
very  prolific  source  of  error  in  this  respect  is  the  practice,  that  has*  now 


FUMIGATION   DOSAGE. 


9 


become  almost  universal,  of  estimating  the  dose  before  the  tent  is  on  the 
tree.  According  to  the  arrangement  of  the  branches,  trees  will  respond 
very  differently  to  the  pressure  of  the  weight  of  the  tent. 

The  diagrams  (Figs.  4  and  5)  illustrate  the  method  of  plotting  the 
dosage   of   trees   as   used   in   the   study   of  the  data  accumulated  for 

this  investigation.  Fig.  4 

shows  the    estimates    of 

*****  forty-eight  trees  made  by 

one  of  the  fumigators  at 

«i        Ontario,  and  is  about  as 

"**  uniform  as  any  we  have 

found.    The  oblique  lines 

indicate  the  size  of  the 

tree,   and   the    numbers 

the  dose.     It  will  be  seen 

that  the  same  sized  tree 

was  judged  to  require  in 

one    case    a    dose    of  3 

Fig.  4.    Dosage  of  fumigation  tents  plotted  on  curves  showing   ounces    and  in  others  3^ 

and  4.  Likewise  practi- 
cally the  same  sized  tents  might  be  supposed  to  require  4,  4-J,  or  5 
ounces;  or  again,  we  find  4-§,  5,  5-§,  and  6^  ounces  all  for  about  the  same 
sized  tent.  It  is  usual  to  find  much  worse  cases  than  this,  as  is  shown 
in  Fig.  5. 

The  success  of  any  method  of  treatment  depends  in  a  large  measure 
on  the  proper  strength  of  the  insecticide  used.     Fumigation  particularly 


Fig.  5.    Dosage  of  two  fumigators  plotted  as  above. 

requires  this,  because  an  under  dose  does  not  kill  at  all.  It  would 
appear  that  two  changes  must  be  made  to  insure  uniformity  in  dosage: 
first,  estimation  after  tenting,  and,  second,  estimation  from  actual 
measurements. 


10 


UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION. 


SMALL   VS.    LARGE    TREES. 

All  the  tables  of  dosage  that  have  so  far  appeared  for  the  guidance  of 
fumigators  have  intended  to  give  the  volume  of  the  tents  in  terms  of 
ounces.  Some  have  by  faulty  calculation  increased  the  dose  of  smaller 
trees  and  decreased  that  of  the  larger  ones.  In  actual  practice  this 
modification  of  the  two  ends  of  the  table  is  regularly  followed.  No  one 
has  attempted  to  determine  how  much  the  practice  of  dosage  varied 
from  the  calculated  volume  of  the  tent,  but  every  one  who  has  attempted 
to  measure  at  all  knows  that  such  variation  exists.  In  the  following 
table  we  have  attempted  to  tabulate  the  results  of  our  measurements  so 
that  they  will  express  it  as  accurately  as  possible: 

Approximate  Dosage. 

Locality.           ^/s.     %    Twice.  %  Average.  %  Half.  %  Quarter.  %    Eighth.  £™T&8\ 

Orange  (1) 9  72  §y2  69  \y2  30  70 

Escondido  (2)  ....  6^  62  4  63  2%  30  62 

Covina  (4) 6  91  b%  82  4%  86       3                              25  86 

Covina  (5). 7        86       6  91  by2  55  3  67        2                              22  75 

Tustin 7        86        6  83  5  50  2y2  80        2        75        \y2        20  74 

Pomona... SlA  86  3  20  86 

Placentia.... 6  91  by2  15  91 

Glendora 9  67  6  67  4  50        2                               15  61 

Ontario  (4) 5  80  4  75  3  83        2y2                            15  79 

Ontario  (2) 4  75  3  15  75 

Ontario  (1) 6  67  4  75  3  15  71 

National  City  ....  5^  64  3^  71  2^  80        2                              15  72 

Pasadena...'. 4  88  3^  68  2  15  75 

Filmore Zy2  86  3  83  2y2  80        2                              15  83 

Arcadia iy2  67  5  80  4  63        2y2                           14  70 

Escondido 3  50  \y2  67  1  12  58 

Covina  (6) 8        75        6  67  4  75  3  83        2y2    80        2            10  76 

Santa  Ana 6  67  4  75  3  83        2y2    80        2           10  76 

Ontario  (3) 5  60  3  83  2y2  10  71 

Anaheim 6        83        5  80  4  75  3  83        2y2    80        2            10  78 

Orange  (2) 6  42  \y2  77  3^  71        2y2    80        2             9  64 

Duarte ...  5y2  82  \y2  77  ?»y2  71        2y2                            7  77 

Sunny  Slope V/2  71  2y2  80  2  6  75 

Covina  (1) 3^  71  2y2  80  2  75        \y2                            5  75 

Monrovia 4  75  3  83  2^  4  79 

Glendora 3  83  2y2  60  \y2  67        1                                4  70 

Average 82  89  73  76  79  74 

Had  the  fumigators  indicated  in  the  above  table  made  their  doses  in 
proportion  to  the  size  of  the  trees,  all  the  per  cents  given  would  have 
been  50.  Thus,  for  instance,  if  the  fumigator  indicated  as  Covina  (6) 
had  followed  the  directions,  supposing  his  tent  to  be  10  steres  capacity, 
and  required  just  the  dose  given,  4  ounces,  then  a  tree  twice  as  large 
should  have  received  8  ounces  instead  of  9,  and  one  four  times  as  large 
16  ounces  instead  of  8.  Likewise  the  smaller-sized  trees  should  have 
received  2,  1,  and  \  ounces  for  the  tents  one  half,  one  quarter,  and  one 


FUMIGATION    DOSAGE.  11 

eighth,  respectively,  of  the  average-sized  tent,  instead  of  3,  2-J,  and  2 
ounces  which  they  did  receive.  This  fumigator  used  on  an  average  76 
per  cent  as  the  ratio  instead  of  50  per  cent  as  called  for  by  the  tables. 

Every  fumigator  thus  reduces  the  dose  for  his  largest  trees  and 
increases  it  for  the  smaller  ones,  so  that  if  the  practice  shows  an  agree- 
ment in  judgment  upon  any  point  this  may  be  considered  to  be  that 
one.  It  may  be  that  this  unanimity  is  explainable  on  the  ground  that 
it  is  difficult  to  conceive  of  the  rate  of  increase  in  three  dimensions 
when  we  really  see  but  two.  When  looking  at  a  tree  one  only  sees  the 
projected  cross-section.  The  ratio  which  would  express  the  difference 
between  the  volume  and  the  area  of  the  cross-section  is  about  67  per 
cent,  a  figure  quite  near  the  actual  average  ratio  of  the  above  table,  74 
per  cent.  While  it  is  thus  possible  that  this  variation  of  dose  as 
between  large  and  small  trees  may  have  arisen  through  an  error  in 
judgment,  it  may  nevertheless  be  sound  practice,  as  will  be  shown  below. 

LEAKAGE    OF   GAS. 

Fumigation  tents  are  never  perfectly  tight.  The  odor  of  the  gas  is 
always  very  evident  outside  of  the  tent,  even  in  those  that  are  tightest. 
The  lightness  of  untreated  canvas  has  caused  many  fumigators  here  and 
elsewhere  to  use  tents  that  allow  a  very  rapid  escape  of  gas.  This  is 
upon  the  theory  that  the  chemicals  are  cheaper  than  labor.  Whether 
this  is  true  or  not  it  is  evident  that  the  dosage  should  be  very  different 
in  tight  and  in  open  tents.  Probably  the  efficiency  of  the  gas  ceases  as 
soon  as  it  reaches  a  certain  dilution.  The  problem  of  dosage  is  then 
that  of  using  enough  material  so  that  there  will  remain  in  the  tent  gas 
of  the  requisite  strength  to  the  end  of  the  killing  period. 

In  order  to  learn  how  great  in  actual  amount  the  leakage  of  the  gas 
really  was  we  secured  the  cooperation  of  Professor  Colby  of  this  Station, 
and  determined  the  amount  of  cyanogen  present  in  measured  quantities 
of  the  air  drawn  from  the  tent  at  intervals.     The  results  are  as  follows: 

Amount  Present  Amount  Present 

in  in 

First  Period.  Second  Period 

Single  tent,  dry 0.07%  0.02% 

Single  tent,  wet 0.05%  0.01% 

Double  tent,  dry 0.21%  0.03% 

The  tents  used  for  the  above  tests  were  obtained  through  the  kindness 
of  Mr.  C.  M.  Heintz,  of  Los  Angeles,  and  Mr.  W.  F.  Lawson,  of  Covina, 
and  comprised  some  that  had  been  in  actual  use  and  others  that  were 
new.  They  were  of  6-ounce  drilling,  which  is  quite  uniformly  used  for 
small  tents.  The  old  tents  had  been  treated  with  a " tanning"  solution. 
But  little  difference  was  noted  between  the  new  and  the  old  tents  in  the 
escape  of  the  gas.  The  gas  was  drawn  slowly  from  the  tent  and  repre- 
sents its  average  strength  during  the  period. 


12  UNIVERSITY    OF   CALIFORNIA — EXPERIMENT   STATION. 

The  above  experiments  are  not  exactly  comparable  with  each  other, 
as  the  length  of  time  in  the  two  periods  varied,  though  they  represent 
approximately  half  an  hour.  The  amount  of  chemicals  used  was  suffi- 
cient to  produce  about  0.3  per  cent  gas.  The  rate  of  loss  is  therefore  seen 
to  be  very  great  and  rapid.  The  size  of  the  tent  used  was  quite  small, 
only  two  steres  in  capacity,  so  that  the  rate  of  leakage  would  be  much 
greater  than  in  an  average-sized  tent. 

When  the  leakage  is  great,  as  in  the  above  experiments,  it  becomes  the 
most  important  factor  to  be  considered  in  the  dosage.  Under  any  cir- 
cumstances the  dose  to  be  used  should  consist  of  the  quantity  of  chemi- 
cals necessary  to  produce  the  desired  density  of  the  gas  and  enough 
more  to  allow  for  the  leakage  that  will  take  place.  The  first  item  in- 
creases as  the  volume  of  the  tent  increases;  the  second,  as  the  area  of  the 
canvas  increases.  In  the  case  of  two  tents,  one  having  half  the  volume 
of  the  other,  the  dose  of  the  smaller  tent  should  be  one  half,  or  50  per 
cent,  of  that  of  the  larger,  if  we  considered  only  the  first  item.  Since 
the  area  of  canvas  does  not  decrease  so  rapidly  we  would  want  a  higher 
ratio  to  meet  the  requirements  of  the  second  item.  This  ratio  is  70  per 
cent.  The  true  ratio  would  seem,  therefore,  to  be  somewhere  between 
50  and  70  per  cent,  unless  some  other  factor  that  we  do  not  now  suspect 
also  enters  into  the  calculation.  This  is  considerably  lower  than  the 
average  of  the  actual  practice. 

EFFECT    OF    MOISTURE. 

Fumigators  differ  fundamentally  in  their  views  as  to  the  relation  of 
moisture  to  the  efficiency  of  fumigation.  Some  would  be  inclined  to 
increase  the  dose  and  others  to  diminish  it  in  foggy  weather.  This  is  a 
matter  of  theory  rather  than  one  of  practice  with  them,  however. 
Usually  no  attention  is  paid  to  the  matter  in  the  practical  working  of 
their  outfits,  except  that  when  the  tents  become  very  wet  and  heavy 
fumigation  is  stopped  because  of  the  difficulty  of  handling  them. 

The  experiment  given  above  with  a  wet  tent  shows  that  this  may  be 
a  very  important  factor.  The  gas  is  so  readily  absorbed  by  moisture 
that  it  disappeared  from  the  air  within  the  tent  more  rapidly  and  com- 
pletely than  through  the  walls  of  the  dry  tent.  This  is  one  of  the 
points  that  should  be  carefully  investigated. 

PRODUCTION   OF   THE   GAS. 

The  generation  of  the  gas  is  a  rather  simple  chemical  reaction,  but  is 
not    generally    understood    by    fumigators.     The    chemical    elements 
involved  and  their  approximate  atomic  weights  are  as  follows: 
Hydrogen   (  H )  =     1  Sodium       (Na)  =  23 

Carbon        (  C  )  =  12  Sulfur  (  S  )  =  32 

Nitrogen     (  N  )  =  14  Potassium  (  K  )  ==  39 

Oxygen       (  O  )  =  16 


FUMIGATION   DOSAGE. 


ia 


If  pure  potassium  cyanide  were  used  the  formula  would  read : 


CHEMICALS   USED 

One  Part 

Potassium 

Cyanide. 

by  weignt. 

One  Part 

85  per  cent 

Sulfuric  Acid  by  volume 

or  1.8  parts  by  weight. 

Two  Parts 

Water 
by  volume 
or  weight. 

K    C   N+H2S04  -     H20 

7  H20 

39    12    14 

2    32    64             2    16 

2     16 

• v ' 

v y '                                    * „ ' 

» v ' 

65 

98                       18 

7  X  18 

no7 

726 

Hydro- 
Cyanogen 
Gas. 


RESULT. 

Residue  of 

Acid-Potassium 

Sulfate 

dissolved  in 


HON    H  K    S  04 

1    12    14      1    39    32    64 


Water. 

8  H20 

2    1& 


27 


136 


The  material  which  is  actually  on  the  market  and  sold  as  pure  98  per 
cent  potassium  cyanide  is  really  a  mixture  of  potassium  and  sodium 
cyanides,  and  Professor  Colby  finds  by  analysis  that  it  contains  about 
4  per  cent  of  impurities  and  30  per  cent  of  sodium  cyanide.  Leaving 
out  the  impurities,  the  formula  would  be : 


One  Part 

Sodium  and  Potassium 

Cyanide 

by  weight. 

85 

One  Part                              Two  Parts 
per  cent  Sulfuric  Acid  by                Water 

volume                             by  volume  or 
(1.8  parts  by  weight).                      weight. 

produces  : 

2KCN 

+  Na  C    N  +  3  H2  S  04  +  3  H2  0  +   22  H2  0 

= 

39  12   14 

23    12    14 

2    32    64                 2    16                    2    16 

* y ' 

» v > 

^ , '                                                                » y '                                                                                "• y ' 

2X65 

49 

3  X  98                   3  X  18                  22  X  18 

130 

294                         54 

179 

348                                       396 

Hydro-Cyanic 

Acid  Gas. 
41  per  cent  of 
Cyanide  used. 

and           Residue  dissolved  in  Water. 
Acid                                      Acid 
Potassium                             Sodium 
Sulfate.                               Sulfate. 

Water. 

3  H  C    N 

+ 

2  H  K    S  04    +    HNa  S  04    + 

25  H2  0 

1     12     14 

1    39    32    64                 1    23    32    64 

2    16 

3X2T 

2  X  136                               120 
272 

25  X  18 

81 


392 


450 


In  the  above  formulae  the  weight  of  the  various  substances  is  calcu- 
lated out  by  the  atomic  weights,  and  shows  that  the  formula  com- 
monly used — one  part  of  cyanide,  one  of  acid,  and  two  of  water — is 
correct  whether  one  has  the  pure  potassium  cyanide  or  the  mixed 
potassium-sodium  cyanide  now  on  the  market.  The  sulfuric  acid  used 
usually  runs  nearer  90  per  cent,  which  insures  a  sufficiency  of  the  acid. 


PROPOSED  DOSAGE  SYSTEM. 

As  the  result  of  this  study  of  fumigation  methods  we  are  in  a  position 
not  only  to  call  attention  to  the  imperfections  of  the  existing  system  of 
guesswork  in  the  estimation  of  dosage,  but  to  have  some  basis  for 
definite  recommendations.  These  recommendations  must  be  considered 
as  only  tentative,  since  they  are  based  chiefly  on  observations  of  actual 
field  practice  and  the  results  have  not  been  verified  by  careful  deter- 
minations. 


1  4  UNIVERSITY    OF   CALIFORNIA — EXPERIMENT    STATION. 

The  base  of  the  system  of  dosage  suggested  is  that  in  which  the  prac- 
tice has  most  likely  been  correct,  viz.,  the  average  dose  of  an  average 
tent.  The  doses  assigned  to  the  average-sized  trees  with  which  the 
various  fumigators  were  working  is  given  in  the  diagram  on  page  6.  By 
taking  the  average  of  these  we  obtain  the  starting  point  for  the  calcu- 
lation of  the  proposed  scheme.  This  average  is  a  4^-ounce  dose  for 
a  14-stere  tent.  This  might  be  considered  a  minimum  dose,  since  it  is 
possible  that  more  have  erred  by  using  too  little  than  too  much.  This 
dose,  however,  is  nearly  a  third  larger  than  the  original  recommendation 
of  Mr.  Morse  in  Bulletin  No.  71  of  this  Station.  All  the  recent  recom- 
mendations for  fumigation  work  in  California  have  been  weaker  than 
the  Morse  table.  The  present  practice,  however,  as  we  found  it  the  last 
season,  has  certainly  approved  the  increase. 

The  ratio,  or  the  relation  between  the  dosage  of  tents  of  different  size, 
is  indicated  in  per  cents  in  the  diagram  just  referred  to.  Here  the 
ratio  given  is  that  between  the  dosage  of  tents  of  such  size  that  one 
has  half  the  volume  of  the  other.  This  ratio  in  the  present  practice 
is  probably  much  too  large,  still  it  is  more  than  likely  that  a  figure 
above  50  per  cent,  which  is  the  ratio  that  has  heretofore  been  recom- 
mended, is  really  justifiable.  The  writer  would  suggest  tentatively  the 
ratio  70  per  cent,  the  largest  figure  for  which  there  appears  to  be  any 
reason.  This  figure,  though  a  great  departure  from  former  recommen- 
dations, is  still  below  the  ratio  of  the  actual  practice  of  about  three 
fourths  of  our  fumigators. 

The  following  table  will  show  how  much  the  dosage  system  here 
suggested  differs  from  previous  recommendations: 

Size  of  tent,  in  meters- 
Distance  over  tent. ._ 13.73  10.86  8.64  6.87  5.40  4.32  3.39 

Distance  around  tent 18.30  14.48  11.52  9.16  7.20  5.76  4.52 

Volume  of  tent,  in  steres 108  56  28  14  7  3.5  1.75 

Dose,  in  ounces — 

By  Morse  schedule  .    25.6  12.8  6.4  3.2  1.6  0.8  0.4 

Present  suggestion 12.7  8.9  6.2  4.3  3.1  2.2  1.1 

PROPOSED   SCHEME   OF    MEASURING. 

The  measurement  and  calculation  of  the  dosage  according  to  any  of 
the  proposed  schemes  present  some  very  considerable  practical  diffi- 
culties. The  measurement  of  height  and  diameter  required  for  most 
tables  of  dosage  can  not  be  made  rapidly  enough  to  be  satisfactory. 
The  measurement  suggested  in  Bulletin  No.  122  of  this  Station  (that  is, 
the  distance  over  and  that  around  the  tent)  can  be  taken  with  sufficient 
rapidity  by  the  method  described  on  page  4  of  this  Bulletin.  It  requires, 
however,  considerable  skill  and  activity.  By  either  method  there  remains, 
after  the  measurements  are  taken,  the  necessity  of  calculation.  To  do 
this  by  mathematics  is   of  course  out   of  the  question.     The   actual 


FUMIGATION    DOSAGE. 


15 


volume  can  be  determined  quickly  and  accurately  by  the  use  of  the 
diagram  (Fig.  2)  given  above,  and  a  series  of  curves  could  be  made 
which  would  give  the  dose  at  once  instead  of  the  volume. 

It  is  very  desirable,  however,  to  avoid,  if  possible,  the  need  of  the  use 
of  tables  and  measuring  apparatus.  Very  decided  progress  in  this 
direction  has  been  made  by  Mr.  W.  H.  Payne,  of  Monrovia,  who  has 
invented  a  tent  marked  off  with  concentric  rings  giving  the  distance 
over  the  top  of  the  tent  in  terms  of  the  dose  required.  This  scheme 
should  work  well  if  proper  arrangements  are  provided  for  coordinating 
the  second  measurement,  that  around  the  tent. 

A  scheme  devised  by  the  writer  several  years  ago  in  Florida  for  use 
in  fumigating  against  the  white  fly  seems  to  solve  the  problem  quite 


-*SS3CV=>Lr 


Fig.  6.    Fumigation  tents  marked  to  indicate  dosage. 


satisfactorily.  It  consists  in  making  a  series  of  parallel  lines  near  two 
opposite  edges  of  the  tent,  which  are  so  distanced  from  the  center  point 
that  they  shall  correspond  with  the  dosage  of  a  tree  of  the  average 
shape.  Upon  these  lines  will  be  placed  numerals  indicating  the  dose, 
the  circumference  in  yards  (paces),  and  the  difference  (that  is,  the 
amount  the  dose  must  be  varied),  should  the  distance  around  be  more 
or  less  than  the  amount  indicated  for  an  average  tent.  This  plan 
would  permit  the  estimation  of  the  dosage  with  sufficient  rapidity  and 
a  fair  degree  of  accuracy.  If  the  tent  is  not  put  on  the  tree  so  that  its 
center  is  directly  over  the  center  of  the  tree,  the  same  dosage  line  may 
not  touch  the  ground  on  the  two  sides,  but  the  average  of  the  two  will 


16  UNIVERSITY    OF   CALIFORNIA — EXPERIMENT    STATION. 

give  approximately  the  correct  measurement.  A  lateral  displacement 
will  give  no  trouble  if  the  rule  is  followed  when  more  than  one  line 
touches  the  ground  on  one  side,  of  using  the  one  indicating  the  highest 
dosage. 

The  following  table  gives  the  scheme  of  marking  tents: 

Numerals  to  be  marked  on  the  lines. 


Distance  from 

Center  of  Tent. 

Ft.        In. 

2 

5 

3 

1 

5 

3 

6 

5 

7 

6 

8 

5 

9 

3 

10 

10 

8 

11 

4 

12 

8 

13 

10 

14 

11 

16 

17 

18 

18 

11 

Ounces. 

Paces. 

\ 

Difference. 

K 

3 

.1 

1 

4 

.2 

IK 

5 

.3 

2 

6 

.3 

2K 

7 

.4 

3 

8 

.4 

sy2 

9 

.4 

4 

10 

.4 

4^ 

11 

.4 

5 

12 

.4 

6 

13 

.5 

7 

14 

.5 

8 

15 

.5 

9 

16 

.6 

10 

17 

.6 

11 

18 

.6 

12 

19 

.7 

This  whole  series  of  lines  would  not  be  all  placed  on  any  one  tent 
ordinarily,  but  only  those  useful  for  the  given  size  of  tent.  Thus,  for  a 
20-foot  tent  the  lines  corresponding  to  a  dose  of  1-J  to  4  ounces  would 
be  useful;  for  a  30-foot  tent,  2|  to  8  ounces,  and  for  a  40-foot  tent,  4  to 
12  ounces  would  be  about  the  range.  The  appearance  of  these  lines  on 
a  tent  is  shown  in  Fig.  6. 

The  use  of  the  tent  will  be  evident  from  the  following  example: 
Suppose  the  lines  on  the  ground  at  the  two  sides  of  a  tree  showed  7  and 
9  ounces,  respectively,  and  the  number  of  steps  around  the  tent  was  17. 
The  correct  dosage  would  be  9  ounces.  The  average  between  7  and  9 
would  have  indicated  8  ounces,  but  the  distance  around  was  two  steps 
more  than  15,  the  number  opposite  the  8  ounces,  and  the  difference 
that  should  be  added  for  each  of  these  is  0.5  of  an  ounce. 

RESUME. 

The  present  study  is  the  result  of  an  extensive  series  of  measurements 
to  determine  what  the  present  actual  fumigation  practice  is  in  the 
matter  of  dosage. 

The  apparatus  used  for  measuring  tents  was  a  wire  line  manipulated 
by  means  of  a  fishing-rod. 

The  dimensions  thus  obtained  were  then  plotted  on  cross-section 
paper,  and  the  volumes  obtained  by  the  use  of  a  system  of  curves. 


FUMIGATION    DOSAGE.  17 

A  striking  difference  in  the  practice  of  fumigators  of  the  different 
counties  was  noticed,  corresponding  somewhat  with  the  history  of  fumi- 
gation practice  in  their  regions. 

No  fumigator  was  found  who  could  make  accurate  estimates  of  the 
volume  of  a  tent,  showing  that  uniform  results  require  that  actual 
measurements  be  made. 

All  fumigators  agree  in  giving  large  trees  a  relatively  heavier  dose 
than  a  small  tree  receives  per  unit  of  volume. 

The  rate  of  leakage,  which  has  not  heretofore  been  taken  into  consid- 
eration in  planning  schemes  of  fumigation  dosage,  was  shown  to  be  very 
large,  and  gives  some  reasons  for  the  larger  dosage  of  small  trees. 

Moisture  was  shown  to  have  a  great  influence  on  the  gas  content,  but 
how  it  might  affect  dosage  remains  yet  to  be  determined. 

The  calculation  of  the  reaction  in  the  generation  of  the  gas  shows 
that  the  proportions  of  cyanide  and  acid  commonly  used  are  correct. 

A  system  of  dosage  based  on  the  average  of  the  measurements,  and 
with  a  ratio  approaching  the  actual  practice,  is  proposed;  and  finally — 

A  scheme  is  presented  for  marking  fumigation  tents  so  as  to  insure 
accurate  dosage. 


REPORTS  AND  BULLETINS  AVAILABLE  FOR  DISTRIBUTION. 


REPORTS. 


1896.  Report  of  the  Viticultural  Work  during  the  seasons  1887-93,  with  data  regarding 

the  Vintages  of  1894-95. 

1897.  Resistant  Vines,  their  Selection,  Adaptation,  and   Grafting.    Appendix  to  Viti- 

cultural Report  for  1896. 

1898.  Partial  Report  of  Work  of  Agricultural  Experiment  Station  for  the  years  1895-96 

and  1896-97.  J 

1900.    Report  of  the  Agricultural  Experiment  Station  for  the  year  1897-98. 
1902.    Report  of  the  Agricultural  Experiment  Station  for  1898-1901. 

BULLETINS. 

No.  115.  Remedies  for  Insect  and  Fungi.    (Revised.) 

121.  The  Conservation  of  Soil  Moisture  and  Economy  in  the  Use  of  Irrigation  Water. 

125.  Australian  Saltbush. 

127.  Bench-Grafting:  Resistant  Vines. 

128.  Nature,  Value,  and  Utilization  of  Alkali  Lands. 

129.  Report  of  the  Condition  of  Olive  Culture  in  California. 

131.  The  Phylloxera  of  the  Vine. 

132.  Feeding  of  Farm  Animals. 

133.  Tolerance  of  Alkali  by  Various  Cultures. 

134.  Report  of  Condition  of  Vineyards  in  Portions  of  Santa  Clara  Valley. 

135.  The  Potato-Worm  in  California. 

136.  Erinose  of  the  Vine. 

137.  Pickling  Ripe  and  Green  Olives. 

138.  Citrus  Fruit  Culture. 

139.  Orange  and  Lemon  Rot, 

140.  Lands  of  the  Colorado  Delta  in  Salton  Basin,  and  Supplement. 

141.  Deciduous  Fruits  at  Paso  Robles. 

142.  Grasshoppers  in  California. 

143.  California  Peach-Tree  Borer. 

144.  The  Peach-Worm. 

145.  The  Red  Spider  of  Citrus  Trees. 

146.  New  Methods  of  Grafting  and  Budding  Vines. 

147.  Culture  Work  of  the  Substations. 

148.  Resistant  Vines  and  their  Hybrids. 

149.  California  Sugar  Industry. 

150.  The  Value  of  Oak  Leaves  for  Forage. 

151.  Arsenical  Insecticides. 

^  Copies  may  be  had  by  application  to  the  Director  of  the  Experiment 
Station,  Berkeley,  California. 


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